Bipolar disorder is a severe and highly recurrent disorder that is ranked among the top 10 causes of disability worldwide. Despite remarkable advances in the treatment of bipolar disorder, studies consistently document alarmingly high rates of relapse, even among patients who receive, and adhere to, treatment. Additionally, bipolar patients continue to be symptomatic between episodes of illness. These high rates of relapse and continued dysfunction suggest the presence of an underlying process, or multiple processes, that render individuals with bipolar disorder vulnerable to the onset of new episodes of illness. An important public health priority is to identify these processes - a goal with profound implications for improving prevention and treatment intervention outcomes. Several lines of research converge to highlight sleep disturbance as a process of key importance in the onset of both depressive and manic symptoms, and thus in the maintenance of bipolar disorder among patients. To date, however, the pervasively poor sleep that is characteristic of bipolar disorder has received minimal empirical attention. Accordingly, the aim of the proposed research is to investigate a potential mechanism by which sleep is disturbed in bipolar disorder. This program of research provides the first direct empirical evaluation of a central causal mechanism posited by social zeitgeber theory, namely, that sleep disturbance in bipolar disorder is caused by disruptions in social rhythms, which can be triggered by stressful life events (Ehlers et al., 1988;Frank et al., 2000). Specifically, the aim of the proposed program of research is to examine whether sleep is disturbed following the experience of stressful events that disrupt social rhythms, in a sample of carefully screened euthymic bipolar outpatients and matched healthy controls. The occurrence and impact of life events, stability of social rhythms, and quality of sleep, will be measured prospectively over the course of an 8 week period using (1) a daily diary for the assessment of stressful events and stability of social rhythms, and (2) a continuously worn actigraph for the daily assessment of sleep-wake cycles and sleep quality. Semi-structured life stress interviews will be administered to assess subjective and objective impact of the events reported during the daily assessment period. This methodology will allow us to begin to delineate a potentially critical mechanism by which sleep may be disturbed in bipolar patients. The long-term goal of this research is to use the knowledge gained to facilitate translational research with the aim of developing new treatment and new prevention strategies that target sleep disturbance among bipolar patients.